Igneous Rocks Formation Quiz

Crystal Size in Igneous Rocks

• Extrusive igneous rocks have small crystals due to rapid cooling.
• Intrusive igneous rocks have larger crystals resulting from slow cooling.
• Unordered ions in rocks are referred to as glass.

Types of Igneous Textures

• Aphanitic texture: Fine-grained, crystals are too small to see.
• Phaneritic texture: Coarse-grained, crystals are large enough to be visible.
• Porphyritic texture: Mixed, contains both large and small crystals.
• Glassy texture: No crystal structure present.
• Pyroclastic texture: Composed of consolidated rock fragments.
• Pegmatitic texture: Features unusually large crystals due to high volatile content.

Igneous Rock Composition

• Primarily made of silicate minerals, includes Al, Ca, Na, K, Mg, Fe.
• Cooling magma leads to two major groups of silicates:
  • Dark silicates: High in Mg and Fe, low in silica.
  • Light silicates: High in silica, also contain Na, K, Ca.

Types of Igneous Rocks

• Mafic igneous rocks: Dark minerals, high in Mg and Fe, basaltic composition.
• Felsic igneous rocks: Light minerals, high in feldspar and silica, granitic composition.

Classification of Igneous Rocks

• Based on two main components:
  • Composition: Relates to the parent magma.
  • Texture: Reflects the cooling history.

Composition Determinants

• Magma cools over a range of temperatures, minerals form at varying times.
• Bowen’s reaction series illustrates the sequence of mineral formation during cooling.

Rock Cycle Overview

• Three rock types: igneous, metamorphic, and sedimentary are interrelated.
• Processes:
  • Pressure and temperature lead to metamorphic rocks.
  • Melting creates magma, which can solidify into igneous rocks.
  • Crystallization of magma forms solids.

Magma: Parent Material

• Magma is molten rock from Earth’s interior; lava is magma at the surface.
• Extrusive/Volcanic igneous rocks: Form from solidified magma above ground.
• Intrusive/Plutonic igneous rocks: Form from solidified magma below ground.

Texture Formation Factors

• Texture is influenced by:
  • Rate of cooling of magma.
  • Amount of silica present.
  • Quantity of dissolved gas.
• Rapid cooling leads to small crystals, while slow cooling allows for larger crystals to develop.

This quiz explores the cooling rates of magma and their effects on crystal sizes in extrusive igneous rocks. Participants will evaluate how different cooling scenarios influence the characteristics of rocks formed from magma. Test your knowledge on geological processes and rock formation.